The invention relates to a device for removing material from a workpiece, particularly removing a hard dental substance such as tooth enamel or dentine from a tooth, or for removing material from ceramic workpieces, by means of a laser.
Devices of this type are known from, for example, DE 41 28 617, GB 01 25 944, U.S. Pat No. 5,020,995, DE 4 038 809, DE 34 15 293 and DE-GM 92 01 056.3, and employ pulsed laser radiation with pulse lengths of either less than 100 ns or greater than 100 .mu.s to remove hard dental substances. The focus size of the laser beam, in other words the expansion of the laser beam on the irradiated workpiece surface, is relatively large, namely between 0.2 and 1.5 mm. It is also known from the cited publications to counteract contamination of the end optics by blasting it free with a water/air spray. It is also known from DE 39 11 871 to use a water/air spray to cool the laser process, which results in a distinct qualitative improvement in the ablation result.
DE 42 11 233 describes a device of this type for removing a hard dental substance, which has an Er:YAG laser that is integrated into a treatment chair and a handle part for positioning the laser beam, with the laser and the handle part being connected by a mirror articulated arm.
In the context of such devices for removing material, it is also known to guide the laser beam line by line over the ablation area (scanning) for attaining uniform material removal.
A disadvantage of the known devices for machining hard dental substances is re-crystallized deposits on the surface of the cavity formed by the radiation. Another problem associated with removing material from teeth is that, as the removal area deepens, the removal rate increases dramatically in the transition from the tooth enamel to the dentine, which may surprise the patient and, in the known devices, can lead to an accidental pulpotomy. A further disadvantage of the known devices is that the relatively high pulse energies give rise to shock waves that may damage the tooth pulp.